Halide abstraction

Monomeric thiazyl halides can be stabilized by coordination to transition metals and a large number of such complexes are known (Section 7.5). In addition, NSX monomers undergo several types of reactions that can be classified as follows (a) reactions involving the n-system of the N=S bond (b) reactions at the nitrogen centre (c) nucleophilic substitution reactions (d) halide abstraction, and (e) halide addition. Examples of each type of behaviour are illustrated below. 

The cation [NSO(NPCl2)2] (14.11) is the proposed intermediate in this ring-opening polymerization process. This cation is extremely reactive, as illustrated by the isolation of the solvent-derived product 14.12 when it is generated by halide abstraction from the cyclic precursor with AICI3 in l,2-dichloroethane. °... 

The converse of polymerization is heterolytic bond scission leading either to R3Sn+ or R3Sn species. Tricoordinate organotin(IV) cations can readily be synthesized at room temperature by hydride or halide abstraction reactions in benzene or other solvents.For example, with R = Me, Bu or Ph ... 

The strong halide-abstracting properties of acidic (X(A1C13) = 0.67 ... 

The mechanism involves a Pd(0) monocoordinate complex as the active species that undergoes oxidative addition to the aryl halide [141]. Thereafter, coordination of the amine to the palladium centre and deprotonation by the external base results in halide abstraction. After reductive elimination, the coupling product is obtained and the catalytic active species regenerated (Scheme 6.45). 

Halide abstraction reactions with these carborane derivatives gives sometimes intermediate products rather than metathesis, as in the reaction of Ag(6,7,8,9,10-Br5CB9H5)(r/2-C7I Ix) with [IrCl(CO)(PPh3)] that yields an Ir—Ag adduct (238),1350 or the reaction of [MoCpI(CO)3] with Ag(CBnH12) which gives (239).I357 135 ... 

Construction of isolated or benzannulated five-membered rings of NHPs can be accomplished by means of various condensation or cycloaddition reactions all of which involve interaction of an electrophilic Pj and a nucleophilic C2N2 building block. Salts containing 1,3,2-diazaphospholide anions or 1,3,2-diazaphospholenium cations can be directly accessed by some of these reactions but the products are in most cases neutral 1,3,2-diazaphospholes or NHP. A particularly concerted effort has been directed toward the synthesis of P-halogen-substituted NHP which are capable of undergoing further reactions via halide displacement or halide abstraction and serve thus as entry points for the preparation of a wide variety of neutral and cationic NHP derivatives. 1,3,2-Diazaphospholide anions are normally accessed by deprotonation of suitable iV-H-substituted precursors. 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

Heterocyclic phosphines 32 were prepared from base-induced condensation of a secondary 1,8-diamino-naphthalene with phosphorus trichloride (the corresponding As- and Sb-analogues were obtained analogously) and converted into cyclic phosphenium cations 33 by Lewis acid promoted halide abstraction using GaCl3 or trimethylsilyl triflate as reagents (Scheme 18) [15, 92],... 

A truly co-catalytic effect of ionic liquids is observed with those ionic liquids displaying a certain latent or real Lewis-acid character. These ionic liquids are usually formed by the reaction of a halide salt with a Lewis acid (e. g. chloroaluminate or chlorostannate melts). In many examples, the Lewis acidity of an ionic liquid has been used to convert the neutral catalyst precursor into the active form of the catalyst by halide abstraction (see Scheme 7.1) [39]. 

Thiazyl halide monomers undergo a variety of reactions that can be classified under the general headings (a) reactions involving the 7i-system of the N = S triple bond, (b) nucleophilic substitution, (c) halide abstraction, and (d) halide addition. The cycloaddition of NSF with hexafluoro-1,3-butadiene provides an example of a type (a) reaction. 

The technique of performing halide abstraction via interaction of a metal halo complex with a silverd), thallium(I), or nitrosonium salt (see ref. 142, for discussion) has proved useful in the isolation of many novel sulfoxide complexes. Thus, [Pd(S-Me2S0)2(0-Me2S0)2]-... 

Prior syntheses of long-lived perhalomethyl cations have been achieved by halide abstraction by use of either a strong Lewis acid (in superacidic or S02C1F solvent media) or Ag+ (vide supra), but no routes to such carbocations through oxidative removal of a halogen bound to carbon were known. The objectives of the current work have been to provide structural and spectroscopic data that, thus far, have been lacking for these systems, and to provide oxidative routes to... 

The strong halide-abstracting properties of acidic XlAlC ) = 0.67 [BMIMjCl/AlCF have been used for the synthesis of the piano stool complexes [Mn(CO)3(Ti -arene)] (Scheme 6.1-7) [12]. 

Grignard reagents can be used to make organosilicon, -germanium, -tin, and -lead compounds by halide abstraction from the corresponding halo-... 

Fluoride complexes of organometallics can be readily prepared by halide abstraction reactions. The general reaction scheme for a carbonyl species ... 

This powerful halide-abstracting ability results in SbFs being the strongest Lewis add with which HS03F forms the strongest superacid , the so-called magic add .70 The Sbv halides are excellent Friedel-Crafts catalysts.269... 

Two series of cationic complexes, [Mo(NO)2L4]2+ (L = RCN, py, etc.) and [MoCl(NO)2L3]+ have been prepared by halide abstraction from [MoCl2(NO)2L2] using silver salts in DME (method D). Some members of the series catalyze the polymerization of norbornadiene, whereas the uncharged parent compounds do not.29 The series [Mo(NO)2L4]2+ (L is a displaceable solvent such as THF) may also be obtained by treatment of [Mo(CO)6] with NO[PF6] followed by addition of further ligands such as bipy.29 This latter reaction also gives [ Mo(NO)2(PF6)2 ] which is assumed to be a polymer with weak PF6 bridges.29... 

In each instance, the events indicated by eurved arrows can occur synchronously or discretely. If substituents have high migratoiy aptitudes, or can facilitate halide abstraction by resonance-stabilization, the first route should bo favored. If tbe substituents lack this... 

Salient features of the cationic pathway, which was introduced independently by Cabri [8] and Hayashi [9], are presented in Scheme 8G.20. Thus, subsequent to oxidative addition, a vacant coordination site is generated either by triflate dissociation or by halide abstraction by the Ag(I) salt in intermediate 20,4. This vacant coordination site facilitates double-bond coordination to form cationic intermediate 20.5, which ultimately forms the Heck product. 

The first homoleptic carbonyl cations of Group 7 metals with the general formula [M (CO)6]+ (M = Mn, Tc, Re) were generated by Fischer and co-workers992 993 and Hieber and co-workers994 995 in the 1960s"6,997 applying halide abstraction by Lewis acids [Eq. (4.236)]. 

Scheme 23 Reagents and conditions (i) CH2Cl2 (ii) CH2X2 (X = Br, I), —80 °C (iii)reductive coupling (iv) oxidative addition (v) SN2 (vi) halide abstraction (vii) migratory insertion (viii) CD2Cl2, r.t.

Zr(IV) and Hf(IV) mono-Cp complexes, 4, 833 Halicholactone, via ring-closing diene metathesis, 11, 230-232 Halide abstraction... 

Mono(cyclopentadienyl) halides, with Ti(IV) alkyl- and alkenyl-substituted Cp ligands, 4, 383 boryl-Cp ligands, 4, 392 halide abstraction reactions, 4, 405 hydrolysis reactions, 4, 398 metathesis reactions, 4, 400... 

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